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EXTOXNET primary files maintained and archived at Oregon State
Revised June 1996
Trade and Other Names:
Trade names include Bay 94337, Bay DIC 1468, Lexone, Sencor,
Sencoral, and Sencorex.
Metribuzin is a slightly toxic compound in EPA toxicity class
III. It is a General Use Pesticide (GUP). Products containing
metribuzin must bear the Signal Word CAUTION.
Metribuzin is a selective triazine herbicide which inhibits
photosynthesis of susceptible plant species. It is used for
control of annual grasses and numerous broadleaf weeds in field
and vegetable crops, in turfgrass, and on fallow lands.
Metribuzin is available as liquid suspension, water dispersible
granular, and dry flowable formulations.
is available as liquid suspension, water dispersible granular,
and dry flowable formulations.
- Acute toxicity: Metribuzin is slightly
toxic via the oral route, with reported oral LD50 values
of 1090 to 2300 mg/kg in rats, 700 mg/kg in mice and 245
to 274 mg/kg in guinea pigs [6,15]. It is practically
nontoxic dermally, with a dermal LD50 of 20,000 mg/kg in
rabbits [6,15]. The 4-hour inhalation LC50 for metribuzin
in rats is greater than 0.65 mg/L, indicating moderate
toxicity via the inhalation route . Metribuzin has
been shown not to irritate the skin or eyes of rats,
rabbits, guinea pigs, or human volunteers [15,32].
Effects of high acute exposure in metribuzin poisoned
rats included narcosis (stupor) and labored breathing.
Deaths occurred within 24 hours, and survivors recovered
slowly without permanent effects .
- Chronic toxicity: No ill effects were
observed in dogs fed dietary doses of 12.5 mg/kg/day for
3 months . No effects were apparent in rats receiving
2.5 mg/kg/day over 3 months, but doses of 25 and 75
mg/kg/day caused enlarged livers and thyroid glands .
In 2-year feeding studies with rats and dogs, results
showed no observable effects at doses of 5 mg/kg/day in
rats and 2.5 mg/kg/day in dogs. Reduced weight gain, an
increase in the number of deaths, blood chemistry
changes, and liver and kidney damage were observed in a
2-year study in which dogs were given 1500 ppm or 37.5
mg/kg/day of metribuzin .
- Reproductive effects: Doses of 15, 45,
or 135 mg/kg/day of technical metribuzin were
administered by gavage to rabbits on days 6 through 18 of
pregnancy. No effects on the mothers were observed at a
dose of 45 mg/kg, but 135 mg/kg lowered maternal weight
gain . No effects on the fetuses were observed at any
of the doses tested . A three-generation study in
rats at doses of up to 15 mg/kg/day (the highest dose
tested), showed no influence on reproduction [32,36].
Metribuzin does not cause reproductive effects.
- Teratogenic effects: In rats, reduced
fetal body weights were seen at doses of 70 mg/kg/day,
and developmental delays were observed at doses of 200
mg/kg/day . Metribuzin did not show teratogenic
activity in rabbits at doses of up to 85 mg/kg/day, but
did decrease weight gain in offspring . These data
suggest that metribuzin is unlikely to cause teratogenic
effects in humans under normal circumstances.
- Mutagenic effects: Tests on live animals
and on tissue cultures have shown that metribuzin has no
mutagenic activity [15,32].
- Carcinogenic effects: There were no
indications of carcinogenic effects in rats receiving
dietary doses of up to 15 mg/kg/day for 2 years, nor in
mice fed up to about 380 mg/kg/day for 2 years .
These data suggest that metribuzin is not carcinogenic.
- Organ toxicity: In single high dose
studies, metribuzin appears to depress the central
nervous system. Other studies indicate that the target
organs of metribuzin are the thyroid gland and the liver.
- Fate in humans and animals: After
metribuzin is absorbed, it is rapidly distributed in the
body and excreted unchanged in the urine . In mammals,
90% elimination occurs within 96 hours, about equally
distributed between the urine and feces .
- Effects on birds: Data indicate that
metribuzin is moderately to slightly toxic to birds. The
acute oral LD50 values are about 100 to 200 mg/kg in
bobwhite quail, mallard ducks, and Japanese quail [6,15].
The reported 5- to 8-day dietary LC50 values for these
species are all greater than 4000 ppm [6,15].
- Effects on aquatic organisms: Metribuzin
is slightly toxic to fish. The 96-hour LC50 is 64 to 76
mg/L in rainbow trout, 80 mg/L in bluegill sunfish, and
greater than 10 mg/L in goldfish [6,15]. The reported
48-hour LC50 in Daphnia magna is 4.5 mg/L, indicating
similar toxicity . The 96-hour LC50 in
marine/estuarine shrimp is 48.3 mg/L .
- Effects on other organisms: It is
nontoxic to bees . Metribuzin may be phytotoxic to
non-target plant species [6,15].
- Breakdown in soil and groundwater:
Metribuzin is of moderate persistence in the soil
environment . The half-life of metribuzin varies
according to soil type and climatic conditions. Soil
half-lives of 30 to 120 days have been reported; a
representative value may be approximately 60 days .
Metribuzin is poorly bound to most soils and soluble in
water, giving it a potential for leaching in many soil
types . Soil mobility is affected by many
site-specific variables, including the amount of soil
organic matter, particle size distribution, porosity,
rainfall, and application rates. Metribuzin has been
detected in Ohio rivers and Iowa wells and groundwater
[35,34]. The major mechanism by which metribuzin is lost
from soil is microbial degradation. Losses due to
volatilization or photodegradation are not significant
under field conditions [3,6].
- Breakdown in water: The half-life of
metribuzin in pond water is approximately 7 days . If
present, metribuzin would most likely be found in the
water column rather than the sediment, due to its low
binding affinity and high water solubility.
- Breakdown in vegetation: Metribuzin is
absorbed through the leaves when plants are given surface
treatment, but the primary route for uptake is through
the root system. From the roots, it is translocated
upward, becoming concentrated in the roots, stems, and
leaves of treated plants. In non-susceptible plants it is
deaminized to more water-soluble conjugates; in
susceptible plants it is not metabolized and disrupts
phosynthesis in the chloroplast .
- Appearance: Metribuzin is a white,
crystalline solid with a slightly sharp, sulfurous odor
- Chemical Name:
- CAS Number: 21087-64-9
- Molecular Weight: 214.29
- Water Solubility: 1050 mg/L 
- Solubility in Other Solvents: s. in
aromatic and chlorinated hydrocarbon solvents, including
dimethyl formamide, cyclohexane, methanol, benzene,
ethanol, xylene, and kerosene 
- Melting Point: 125-126.5 C 
- Vapor Pressure: 0.058 mPa @ 20 C 
- Partition Coefficient: 1.6021 
- Adsorption Coefficient: 60 (estimated)
- ADI: Not Available
- MCL: Not Available
- RfD: 0.025 mg/kg/day 
- PEL: Not Available
- HA: 0.2 mg/L (lifetime) 
- TLV: 5 mg/m3 (8-hour) 
DuPont Agricultural Products
Walker's Mill, Barley Mill Plaza
P.O. Box 80038
Wilmington, DE 19880-0038
- Phone: 800-441-7515
- Emergency: 800-441-3637
References for the information in this PIP can be found in
Reference List Number 8
information in this profile does not in any way replace or
supersede the information on the pesticide product labeling or
other regulatory requirements. Please refer to the pesticide